1. Field of the Invention
This invention relates to a metal film forming method, and more particularly, is applicable to laminating a metal film on a silicon wafer in a desired pattern.
2. Description of the Related Art
Heretofore, the etching method and the lift-off method have been methods for lamination-forming a metal film on a silicon wafer in a desired pattern.
Usually, the etching method is performed such that a metal film is laminated all over the upper surface of a silicon wafer by a method such as sputtering or evaporation. A resist layer is formed on the metal film, avoiding parts which are desired to be reserved for (usually, wiring portions), and then the exposed metal film is etched via the resist layer.
On the other hand, the lift-off method is performed such that a resist layer is formed on the upper surface of a silicon wafer, avoiding parts which are desired to be reserved. A metal film is laminated all over the upper surface of the wafer which includes the upper surface of the resist layer by sputtering, evaporation, etc., and then the metal film which is lying on the resist layer is eliminated (lifted off) from the wafer together with the resist layer.
In the abovementioned conventional lift-off method, it is necessary to cause organic matter, which is used for dissolving the resist layer, to permeate the resist layer sufficiently in order to perform the lift-off process satisfactorily. For this purpose it is necessary that the shape of the cross section of each opening 2A of the resist layer 2 which is formed on the upper surface of the silicon wafer 1 is of an inverse tapered form or bottle neck form, as shown in FIG. 1A or 1B.
Heretofore, various methods have been proposed and realized using a photoresist material and process for obtaining such shapes for each opening 2A of the resist layer 2. However, there have been problems in that such methods are all costly due to the resist material used or other aspects of the methods. Reproducibility of the pattern using such methods is also poor.